Mechanical clamps are commonly used in manufacturing processes to clamp a workpiece in place and to secure the workpiece while it is being machined, welded or otherwise worked.
An example of prior art mechanical clamp apparatus is shown in the Lehmann U.S. Pat. No. 2,537,594 issued Jan. 9, 1951 and in the McKenna U.S. Pat. No. 2,236,439 issued Mar. 25, 1941.
Other prior art mechanical clamps include a pneumatic cylinder for causing clamping movement of the clamping devices of such clamps and holding these clamping devices in clamping engagement with a workpiece. Examples of such mechanical clamps and including fluid cylinders are illustrated in the Blatt patents: U.S. Pat. No. 3,702,185 issued Nov. 7, 1972; U.S. Pat. No. 3,545,050 issued Dec. 8, 1970; U.S. Pat. No. 3,565,415 issued Feb. 23, 1971; U.S. Pat. No. 3,567,208 issued Mar. 2, 1971; U.S. Pat. No. 3,381,954 issued May 7, 1968; U.S. Pat. No. 3,362,703 issued Jan. 9, 1968; and U.S. Pat. No. 3,273,878 issued Sept. 20, 1966. Attention is also directed to The Mericle U.S. Pat. No. 3,302,943 issued Feb. 7, 1967 and the Mericle U.S. Pat. No. 3,347,542 issued Oct. 17, 1967.
In those clamping devices where a fluid cylinder is provided, it is preferred that the fluid cylinder be a pneumatic cylinder rather than a hydraulic cylinder in order to take advantage of the availability of a supply of compressed air in most common manufacturing facilities. If the cylinders used are pneumatic cylinders, the clamping arrangements are substantially less expensive to manufacture since a hydraulic pump is not required. However, one of the problems with the use of pneumatic cylinders for applying clamping force is that mechanical clamps may release the workpiece if the supply of air to the pneumatic cylinder is interrupted. Such mechanical clamps are commonly used to secure a workpiece in place while the workpiece is being machined or otherwise worked. If the pneumatic cylinder releases the workpiece while it is being worked, the electrically driven machine may continue to operate even though the workpiece is released.
Some of the prior art mechanical clamps avoid these problems by employing overcenter toggle arrangements for locking the clamping member into clamping position. During the operation of the overcenter toggles, as the toggle links approach the overcenter position, the toggle links and pins joining the toggle links are subjected to very high loads, and there is deformation of at least some of the parts of the toggle links as they move through the overcenter position. These high loads and deformation of parts can result in substantial wear of the parts and reduces the useful life of the mechanical clamp. Where the mechanical clamp is used in the manufacturing operation to hold the workpiece. the mechanical clamp may be subjected to numerous operating cycles and a long useful life of the mechanical clamp is necessary.